Regeneration of catalysts



June 26, 1962 H. T. PORTER ETAL 3,041,290

REGENERATION OF CATALYSTS Filed March 14, 1955 w a, Zk ami a, if '6) gw -orn cys.

3,041,290 Patented June 26, 1962 nice 3 Claims. (Cl. 252-419) This invention relates to the regeneration of catalysts.

In many catalytic processes, particularly those involving hydrocarbons, combustible deposits, such as carbon and sulphur, form on the catalyst, temporarily destroying its activity. These deposits must be removed periodically by burning with oxygen (usually supplied as air) to restore catalyst activity. To avoid combustion taking place at temperatures so high that damage to the catalyst would occur it is also the practice to dilute the air with steam or an inert gas mixture of nitrogen, carbon dioxide and steam made by burning hydrocarbon gas or oil in a special generator. Further, the steam or inert gas mixture is usually recirculated over the catalyst with the addition of fresh air, an equivalent amount of spent gas being purged olf. A supply of inert gas is then only required for starting up, with a corresponding saving in fuel.

Catalytic processes involving hydrocarbons are often carried out at high pressures and it is often advantageous or desirable to regenerate at high pressures, e.g. 100-500 lb./sq. in. or higher and to recycle the gases with the addition of fresh air. In effecting the changeover from reaction to regeneration in such processes it is common practice to depressure the reactor, purge with an inert gas mixture of the type referred to above, and repressure with such an inert gas mixture. For. this purpose it is known to use an inert gas generator, of the typeburning hydrocarbon gas or oil, which is capable of generating an inert gas mixture at the pressure at which it is desired to carry out the regeneration. Such a high-pressure inert gas generator is diflicult to design and is troublesome in use. In British patent specification No. 708,554 we have described a method of catalyst regeneration which cases the problem of the design of the inert gas generator by enabling a generator working under a lower pressure than the desired regeneration pressure to be used.

The principal object of the present invention is to dispense with the need for a conventional inert gas generator altogether. v

According to the inventon, a method of regenerating catalysts which have become contaminated with combustible deposits and have therefore lost their activity, comprises in sequence the steps of filling the catalyst chamber with a single volume of steam, sufficing in volume for the whole regeneration operation and containing no free oxygen, at an elevated pressure and at a temperature high. enough for combustion of the deposits subsequently to take place, circulating the steam through the catalyst chamber, introducing into the chamber sufficient air or oxygen to maintain the desired oxygen concentration therein and cause combustion of the deposits, and bleeding off sufiicient spent gas to prevent the pressure rising above the desired regeneration pressure.

Preferably the catalyst chamber is initially filled with steam at a pressure 300 500 lb./sq. in.

For catalysts that are relatively insensitive to steam the most advantageous procedure is to fill the catalyst chamber with the steam at the full elevated pressure at which it is desired to regenerate, introduce air or oxygen at the appropriate rate and bleed off an equivalent amount of spent gas.

The gas bled oti initially contains a high proportion of steam and as regeneration proceeds the concentration of steam in the catalyst chamber falls to an equilibrium value depending upon the amount of hydrogen in the deposits. 7

For catalysts that are sensitive to steam, e.g. the fluorine activated autofining catalyst (which is described in British patent specification No. 719,627), it may be undesirable to use steam at the full desired regeneration pressure since damage to the catalyst may occur, and the chamber may therefore be filled with steam at an elevated pressure which is low enough to prevent such damage, the pressure being subsequently built up, as the air or oxygen is introduced, until the desired regeneration pressure is reached, whereupon an amount of spent gas equivalent to the amount of air or oxygen introduced is bled off to maintain the pressure constant. Again the concentration of steam in the chamber falls to an equilibrium value.

In cases where combustible gas remains in the depressured catalyst chamber after the catalytic reaction, it is desirable to remove these gases before starting regeneration and this may be done by purging with steam.

The invention will now be described by way of example with reference to the accompanying drawing.

The reactor 1 (of an autofining unit) containing the catalyst is connected through valves 2 and 3 to the reaction system while valves 4, 6, 7 and 9 are shut. For regeneration, valves 2 and 3 are closed and the reactor depressured by opening valves 4 and 5. Steam at a temperature of about 700 F. is then introduced through valve 6 and the reactor purged of any combustible gases. Valve 5 is then shut and the steam pressure increased until it reaches the desired regeneration pressure, say 400 lb./ sq. in. gauge. Valve 6 is then shut, valve 7 opened and circulation of the steam started by means of a centrifugal blower 8. Air is then added to the system by the variable speed compressor 10 through valve 9 at such a rate that the required oxygen concentration is maintained in the circulating gas for coke and sulphur combustion in the reactor. Valve 5 is then opened to bleed off suificient spent gas to maintain the pressure at the desired level. Regeneration then proceeds until all the coke and sulphur have been burnt off the catalyst.

The heat of combustion of the coke and sulphur is given up to the gas and is removed the cooler or waste heat boiler 11.

As mentioned above, if the catalyst is sensitive to steam at high pressure the introduction of steam via valve 6 is stopped when the pressure in the chamber 1 has reached the level beyond which it is not safe to go. Valve 6 is then shut, circulation started as before and air is added through valve 9 at such a rate that the required oxygen concentration is maintained in the circulating gas. The pressure is built up until the desired regeneration pressure is reached whereupon valve 5 is opened sufiiciently to maintain the pressure constant.

By operating according to the method of the invention the economic advantages of conventional recycle inert gas regeneration over once-through steam-air regeneration are obtained without the need for a conventional inert gas generator.

We claim:

1. A method of regenerating catalysts which have become contaminated with combustible deposits and have therefore lost their activity, comprising in sequence the steps of filling the catalyst chamber with a single volume of steam, sufficing in volume for the whole regenerating operation and containing no free oxygen, at an elevated pressure lower than which it is desired to regenerate and a temperature high enough for combustion of the deposits subsequently to take place, discontinuing the supply of steam when said chamber has been filled with said single from the system by aesneeo above the desired regeneration pressure.

2. A method according to claim 1, in which the catalyst chamber is filled with steam at a pressure of 300-500 lb./sq. in. before circulation of the steam is started.

d 3. A method according to claim 1, in which the free oxygen-containing gas is air.

References Cited in the file of this patent UNITED STATES PATENTS 1,619,327 Backhaus Mar. 1, 1927 1,822,303 Miller Sept. 8, 1931 2,225,402 Liedholm Dec. 17, 1940 2,457,566 Krieger et a1 Dec. 28, 1948 2,495,723 Hermann Ian. 31, 1950 2,509,900 Wormith May 30, 1950 2,762,752 Hemminger Sept. 11, 1956 

1. A METHOD OF REGENERATING CATALYSTS WHICH HAVE BECOME CONTAMINATED WITH COMBUSTIBLE DEPOSITS AND HAVE THEREFORE LOST THEIR ACTIVITY, COMPRISING IN SEQUENCE THE STEPS OF FILLING THE CATALYST CHAMBER WITH A SINGLE VOLUME OF STEAM, SUFFICING IN VOLUME FOR THE WHOLE REGENERATING OPERATION AND CONTAINING NO FREE OXYGEN, AT AN ELEVATED PRESSURE LOWER THAN WHICH IT IS DESIRED TO REGENERATE AND A TEMPERATURE HIGH ENOUGH FOR COMBUSTION OF THE DEPOSITS SUBSEQUENTLY TO TAKE PLACE, DISCONTINUING THE SUPPLY OF STEAM WHEN SAID CHAMBER HAS BEEN FILLED WITH SAID SINGLE VOLUME OF STEAM, CIRCULATING THE STEAM OF SAID VOLUME 